1. Technical Field
The present disclosure relates to devices for bone fixation. More particularly, the present disclosure relates to an occipital plate for cervical fixation.
2. Background of Related Art
The occipitocervical junction, which comprises the occiput, atlas, and axis, represents a unique and complex interface between the cranium and the rostral cervical spine. More than 50% of the rotation and flexion-extension of the head and neck occurs in that region. In addition, the osseous articulations and their ligamentous support structures must resist force in eight axes of rotation. These include flexion, extension, bilateral lateral bending; and bilateral rotation, distraction, and axial loading. Instrumentation constructs not only must resist forces in all of these vectors, but also must resist the significant lever arm created by the suboccipital bone and the cervical spine, which meet at a 50° angle. Any instrumentation construct designed for use in this region must, therefore, have adequate dimensions to interface with the osseous structures of the spinal structures as well as have sufficient rigidity and purchase to resist these forces until bone fusion can occur. Great flexibility must be afforded to allow for the multiple anatomical variations seen in this region.
In the early 1900's occipitocervical instability and lesions located at the occipitocervical junction were considered inoperable and terminal. Since the first description of an occipitocervical fusion by Forrester in 1927, multiple methods of fusion in this region have been described. Descriptions of simple onlay bone grafts with halo immobilization; wire, pin, or hook constructs; rigid metallic loops and rectangles fixed to the bone with either screws or wires; and most recently, plate or rod constructs with screws have all been described. In general, the evolution of this technology has focused on providing increasingly more rigid constructs to facilitate bone fusion and to minimize the need for and duration of external immobilization.
A common technique for fixing occipitocervical instability is the use of an inverted Y-shaped screw plate. Using this technique, the plate is secured to C1-2 with transarticular screws and to the suboccipital bone with paramedian screws. The suboccipital bone varies in thickness, with a mean thickness of about 14 mm. Screws must be carefully selected to provide adequate purchase, yet avoid cerebellar injury. Utilizing the maximum screw length possible is critical, because shorter screws do have reduced resistance to pullout. If stabilization is required below the C1-2 level, then lateral mass screws can be placed through additional holes in a longer plate to include these levels as well. A bone graft is again added to promote fusion. The Y-shaped plate, in combination with transarticular screws, is an economically favorable alternative. Immediate postoperative stabilization is achieved and very low rates of pseudoarthrosis have been reported.